WASHINGTON  Coral reef ecosystems, among the oldest and most diverse forms of life, are declining in U.S. waters because of overfishing, climate change, marine diseases, land-based pollution, storms and grounded ships.

Such ecosystems "clearly are beset by a wide array of significant threats," the National Oceanic and Atmospheric Administration said in a report Thursday.

About three-quarters of all the threats to coral reefs have not changed since the agency's last overview three years ago. Nearly half of those are considered medium to high threats.

Only in one place, Guam, did a threat level go from low to high, because of coral bleaching from rising ocean temperatures.

Coral reefs provide food and shelter to fish and protect shores from erosion.

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The 522-page report says many of the programs that scientists use to monitor coral reefs only began in the past two to five years, so some of the data is inconclusive.

But the agency's head, Conrad Lautenbacher, said the findings offer "a baseline we can use to compare future results."

The data comes from more than 160 scientists and coral reef managers who have monitored the water quality, the sea floor and fish and other species that live in coral. They also have expanded their digital mapping of shallow water coral reef ecosystems.

Globally, only about 30 percent of the world's coral reefs are healthy, according to a study last year by 240 scientists in 96 countries. That is down from 41 percent in 2002.

That report listed global warming -- blamed for higher water temperatures and carbon dioxide concentrations -- as the top threat. It found that the Caribbean had lost 80 to 98 percent of its elkhorn and staghorn coral, which are both among the most common species.